Nails here can be low-cost lamp timers - or in this case one-wire sensors prefitted with cable and properly isolated.

And the issue is that the OP must carefully compute the cost of buying and setting up the test equipment, and the time needed for testing/packaging, together with the potential change in sell price. It isn't always obvious that quality pays. Selling 100 units and giving 5 freebies may be a better deal for both parts. The customer may see it as goodwill to get 103 working and 2 nonworking sensors while paying for 100.